The present invention relates to disk drives, and in particular to CD-ROM drives and mechanisms for controlling the disk drive speed.
CD-ROMs are in use today for a variety of applications. CD-ROMs are disks which have data stored on them in a manner that can be detected by a laser beam in a read head. For instance, the disk could have microscopic dark and light circles indicating bits of data, with one being reflective, and the other being burned through to a non-reflective lower layer. CD-ROMs are read only, but their advantage is that they can store large amounts of data. Typically, they are used for storing audio data for use with stereo systems, or for storing large amounts of archival-type data, such as library books. In addition, they can store multi-media data, such as audio and digital data for use in multi-media platforms.
A typical multi-media platform would include a standard personal computer with a multi-media board, a video board or a sound board. This board will interface with a CD-ROM drive to provide retrieved data to the computer.
The CD-ROM drive itself consists of a motor for turning a spindle which supports the compact disk (CD) itself. A read head including the laser and detector moves back and forth over the disk to detect data at the desired area. Many CD-ROM drives today are multi-speed drives. Multiple speeds are needed because audio data being retrieved for playing over speakers is retrieved at a much slower rate than large volumes of textual or video data being transferred to a computer screen. Thus, many CD-ROM drives will detect the type of disk being inserted and switch the motor to a low speed for an audio disk and to a high speed for a data disk.
One disadvantage of such dual-speed drives compared to the standard audio drives is that the disk drive motor is more expensive since it must be able to stand up to the rigors of the higher speed application, even when used for only the low speed audio. If an inexpensive audio-type disk drive motor is used, the motor may wear out fairly quickly if used for high speed data transfers, such a motor could wear out in one to two years if used for such high speed applications.
In addition to using a more durable, more expensive motor, another solution for saving wear and tear on the motor is to turn the disk drive motor off when it is not being used. This is often used in a sleep mode in portable computers, for instance. In addition to saving wear and tear on the disk drive motor, this also will conserve power. Clearly, more power is required at high speed than at low speed, and more power at low speed than when the disk drive motor is turned off.
Many CD-ROM drives also include a DRAM data buffer for storing the data retrieved from the CD-ROM. This helps match the transfer rate between the CD-ROM and the computer, and also allows a way to even out the uneven transfer from the CD-ROM, which will occur, for instance, when it is in a search mode looking for the appropriate track, at which time no data will be transferred. When it locks on to a track, the data rate is very high. The buffer allows an averaging out of this data transfer rate and also allows time for the CD-ROM drive to perform error correction, rereading of erroneous detected data, etc., without affecting the rate transferred to the computer.
It would be desirable to have a CD-ROM disk drive motor system which can efficiently operate at two speeds with minimal power and minimal wear and tear on the motor.